This concerns a process for controlling a passenger protection system. Examples of processes for controlling a passenger protection system by means of a CPU in conjunction with acceleration signals, taking into consideration the seat occupancy can be found in DE 195 47 333 A1, DE 196 15 321 A1, DE 196 11 073 A1 or DE 197 24 344 C1. Here the triggering of at least one passenger protection device, especially the front passenger airbag, will be inhibited, whatever the acceleration signal, if the central processing unit (CPU) receives a trigger inhibiting signal from one of the seat occupancy detection devices. Contact switches in the vehicle seat, pressure or capacitance sensors, light barriers, echo/reflex procedures or imaging systems are used for this type of seat occupancy detection device.
In addition to this, we are already familiar with manually operated trigger inhibitors, which the driver or the front passenger can use to enable or disable triggering of the passenger protection devices. For example, EP 0 728 636 A1 describes the possibility, despite a seat occupancy detection device transmitting an inhibiting signal, of still being able to switch on the passenger protection device manually.
Here, triggering is usually controlled by means of a CPU with a microprocessor, which is programmed by the software to detect and process the acceleration and trigger inhibiting signals. Unfortunately, with microprocessors, you cannot totally rule out the possibility that a software glitch or interference signals could cause temporary malfunctions. DE 197 43 914 A1 therefore recommends a process for controlling a passenger protection system in which, redundantly to the microprocessor, in an evaluation unit preceding the microprocessor, a release signal for the ignition units will be derived from the acceleration signals if the acceleration signals exceed a predetermined threshold. The ignition units will then only be triggered if both the ignition command and the release signal are present. An acceleration signal processing error in the CPU cannot then lead directly to triggering, at least not until the threshold for the release signal has been exceeded. The circuit of the preceding evaluation unit, for its part, can be clearly designed as a CPU with a microprocessor, so that this evaluation unit is not susceptible to interference and especially not prone to software glitches and interrupts.
In addition to this, DE 196 11 073 A1 also mentions the possibility of the evaluation unit equipped with a microprocessor only detecting the acceleration signals and generating a corresponding trigger signal, while a separate evaluation unit is provided for seat occupancy detection and used to generate a releasing or inhibiting signal, which is logically linked to the trigger signal in a gate circuit, so that if a release signal is present in connection with the trigger signal, the ignition circuit can ignite the airbag.
DE 39 24 595 A1 tells of a control layout for a passenger protection system, where a monitoring circuit monitors the frequency of a test signal generated by a microprocessor and any deviation will prevent triggering of the passenger protection devices, by activating an inhibiting device between the CPU and the passenger protection device.
DE 44 24 020 A1 likewise describes the supervision of a control unit of a safety device by an additional control unit.